The present invention relates to a filter apparatus for removing contaminants from water and, more particularly, to a small demountable filter unit which can be attached to a flexible plastic bottle to filter contaminated water contained in and dispensed from the bottle.
It is known in the art to provide removable and replaceable filter cartridges which may be demountably attached to the neck of a rigid-walled container (such as a canteen) to filter contaminated water dispensed from the container. U.S. Pat. No. 3,335,917 shows a filter element which is inserted into the container and attached to the neck thereof. Water flows through the filter cartridge by gravity and the cartridge includes a concentric air pressure equalization passage extending between the outer attachment cap and the bottom of the filter element.
U.S. Pat. Nos. 5,122,272 and 5,167,819 also show filter cartridges inserted into a canteen-like container and attached to the neck thereof. The filter cartridge includes an integral outwardly extending straw allowing the user to withdraw water through the filter cartridge by suction. A pressure equalization passage is also provided through the outer closure cap and neck of the canteen.
U.S. Pat. No. 5,126,044 shows a filter cartridge which may be threadably attached to the neck of a bottle and mounted externally thereof. This patent teaches that the gravity flow of contaminated water from the inverted bottle through the filter cartridge may be supplemented by providing the bottle with flexible walls and squeezing the same. However, no means for equalizing the negative pressure inside the dispensing bottle is described, apart from allowing external atmospheric pressure to force air in a reverse direction through the filter element. U.S. Pat. No. 4,714,550 shows an internally mounted canteen filter cartridge in which contaminated water in the canteen may be dispensed through the filter under the combined influence of an integral drinking straw and a separate manually operated pump to pressurize the interior.
Other dispensing filters utilizing gravity flow are shown in U.S. Pat. Nos. 4,181,243 and 4,605,499.
A canteen filter or bottle filter of the types described above, if operated by simple gravity flow, requires the use of a very porous filter media or loose packed granular bed. As a consequence, contaminant removal is typically compromised. On the other hand, when such filters function with the use of internal pressurization of the container, a more densely packed and more efficient filter media may be utilized. However, such constructions tend to be more complex and, in particular, require a more sophisticated venting arrangement for equalizing the inherent pressure differential which develops between the interior of the container and the outside atmosphere during dispensing.